Introducing an Effective Method to Reduce Fungal Infection in Mass Rearing Predatory Mites Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae)

Due to the process of quality control of agricultural products and accurate assessment of pesticide residues in products exported to destination countries, the application of biological control has become essential. In order to use biological control, biological agents must either be purchased from countries with the technology of mass production of natural enemies, or to meet the needs of the country, the technology of mass production of predators and parasitoids must be developed. In the case of mass rearing of predatory mites, which are mostly used to control spider mite, the problem of mass prodaction has been partially resolved and some companies are rearing, but in mass rearing of these predators, destructive effects on non-target natural enemies and mold growth on the rearing media of predatory mites are problematic. The predatory mite, Amblyseius swirskii (Athias-Henriot) is one of the most common biological agents for control of two-spotted mite, whitefly and onion thrips in greenhouses, which is widely used in greenhouse crops worldwide. The importance of this study is to facilitate the mass production of this predatory mite. In mass production of this predator, a medium with eggs, nymphal stages, and mature mites of Carpoglyphus lactis Linnaeus was used at 25 ± 1 ° C, 70 ± 5% RH and L: D 16: 8. One of the most important limitation in the production of this predator is infection with some fungi such as Rhizopus spp., Aspergillus spp,and Penicillium spp., which caused the deterioration of the medium and consequently the death of dried fruit mites and predatory mites in the production environment.
To investigate the efficacy of five componds on fungal control, an experiment was achieved with twelve treatments in a completely  randomized design in three replication. From the culture medium (800 g of elm flour, 195 g of wheat bran and 5 g of palm pollen) plus 1g/kg of compounds: tebuconazole, baking soda (sodium bicarbonate), Caliban® (potassium bicarbonate), Chitosan®, and carbendazim and in treatments where two compounds were mixed, 0.5 g/kg was used.
The analysis of variance for the treatments revealed significant differences in fungal infection reduction and the population dynamics of the mites. The treatments that showed the highest reduction in fungal infection compared to the control were treatments 1 (tebuconazole®), 3 (Caliban®), and 6 (Trichocara®), with reductions of 66.33%, 63.25%, and 28.62%, respectively.
In terms of the population increase of the prey mite C. lactis, the treatments that exhibited the highest increases were treatments 1 (tebuconazole®), 10 (Chitosan = tebuconazole), and 6 (Trichocara®), with population increases of 80.22%, 65.75%, and 65.15%, respectively.
Regarding the population increase of the predatory mite A. swirskii, the treatments that showed the highest increases were treatments 1 (tebuconazole®) and 6 (Trichocara®), with population increases of 76.33% and 72.66%, respectively, in the first group. In the second group, treatments 3 (Caliban®), 2 (soda), and 10 (Chitosan + tebuconazole) exhibited population increases of 56.33%, 54.66%, and 53.66%, respectively.
These results demonstrate the effectiveness of treatments 1 (tebuconazole®) and 6 (Trichocara®) in reducing fungal infection and promoting the population growth of both prey and predatory mites. Treatments 3 (Caliban®), 10 (Chitosan = tebuconazole), and 2 (soda) also showed positive effects on the population dynamics of the mites.
The predator mite population of A. swirskii is able to complete its growth on growth substrates with prey mite C. lactis. This predator has a high potential in feeding on dry fruit mite C. lactis. Therefore, this bait can be a suitable food for the mass production of A. swirskii mites. The most important problem in rearing large numbers of predatory mites is saprophytic fungi, which cause the destruction of a large number of predatory mites and their prey due to their sudden expansion. In general, according to the results of our study, the use of tebuconazole fungicide at a rate of one per thousand of commercial material and also the biological compound of Trichocara® (Trichoderma virens) with a concentration of one per thousand are recommended to control saprophytic fungi in mass production environment of predatory mite,A. swirskii,. Each of these two compounds has its advantages and disadvantages. In terms of availability, tabuconazole is more readily accessible compared to Trichocara®, which is a biological compound and considered more environmentally safe. However, Trichocara® may darken the color of the culture medium slightly due to the growth of Trichoderma virens in the medium. Considering the economic aspect and cost reduction in mass production of predatory mites, baking soda and Caliban®, which were part of the second group of effective treatments, offer economic value and are much cheaper than other compounds. They can effectively reduce the severity of fungal infections at minimal cost. Among the different compounds tested, the use of tebuconazole fungicide at a rate of one gram per thousand grams of substrate showed the most significant effect in controlling fungi. Although sodium bicarbonate and potassium bicarbonate were found to be less effective, they are still viable options due to their non-toxic nature.